Data storage media commonly used for storage and retrieval of data come in many forms, such as magnetic tape, magnetic disks, optical tape, optical disks, holographic disks or cards, solid state memory such as flash memory and the like. In magnetic media, data is typically stored as magnetization patterns that are magnetically recorded on the medium surface. The data stored on the medium is typically organized along “data tracks,” and transducer heads are positioned relative to the data tracks to read or write data on the tracks. A typical magnetic storage medium, such as magnetic tape, usually includes several data tracks, which may be grouped together in multiple data bands. Optical media, holographic media, and other media formats can also make use of data tracks.
Servo patterns refer to patterns or other recorded marks on the medium that are used for tracking purposes. In other words, servo patterns are recorded on the medium to provide reference points relative to the data tracks. A servo head detects a servo pattern and sends a signal representing the detected pattern to a servo controller. The servo controller interprets a detected servo pattern and generates a position error signal (PES). The PES is used to adjust the lateral distance of the transducer head relative to the data tracks so that the transducer head is properly positioned along the data tracks for effective reading and/or writing of data to the data tracks.
With some data storage media, such as magnetic tape, the servo patterns are recorded in specialized areas on the medium, called “servo bands.” Servo bands serve as references for the servo controller. Some magnetic media include a plurality of servo bands, with data tracks being located between the servo bands.
The servo patterns recorded in the servo bands may be sensed by one or more servo heads. Once the servo head locates a particular servo band, one or more data tracks can be located on the medium according to the data track's known displacement from the servo band. The servo controller receives signals derived from detected servo patterns from the servo heads and generates PESs, which are used to position a read/write head accurately relative to the data tracks.